Dozing while driving or inattentive driving is derived from a decreased awakening degree of a driver on a vehicle. The decreased awakening degree potentially occurs a serious traffic accident. Therefore, various awakening degree determining systems have been proposed.
For instance, in Patent document 1, enhancing accuracy of an awakening degree determining system is proposed. Here, moving integration values with respect to vehicle behavior detection data such as a steering angle are obtained during a learning period for which a vehicle speed is stabilized to thereby stabilize operating conditions. A threshold value used for determining the awakening degree is then determined based on an average or standard deviation computed from the obtained moving integration values. Obtaining of the moving integration values is continued even after the threshold value is determined. Thereafter, when a value exceeds the threshold value, dozing while driving is determined. Thus, in Patent document 1, deviations of integration values are decreased by obtaining the moving integration values to thereby enhance accuracy of determining of the dozing while driving.
Patent document 1: JP-H11-227489A
Obtaining the moving integration values of the vehicle behavior detection data, described in Patent document 1, is effective in decreasing the deviations of variation of the detected vehicle behavior. However, the vehicle behavior is affected by peripheral traffic environments while the vehicle is actually driven. In particular, the vehicle behavior is clearly differentiated by whether a preceding vehicle is existing or not. Conventional systems such as the system described in Patent document 1 do not consider the influence to the vehicle behavior due to the peripheral traffic environments. This restricts increase of the accuracy for determining the awakening degree of a driver.